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CREATE TABLE simplex.playlists (
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    id uuid,
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    title text,
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    num int,
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    album text,
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    artist text,
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    song_id uuid,
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    PRIMARY KEY (id,title,num)
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    );
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SELECT * FROM simplex.playlists where id=2cc9ccb7-6221-4ccb-8387-f22b6a1b354d ORDER BY title DESC;
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搜索成功
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SELECT * FROM simplex.playlists where id=2cc9ccb7-6221-4ccb-8387-f22b6a1b354d ORDER BY num DESC;
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搜索异常Order by currently only support the ordering of columns following their declared order in the PRIMARY KEY
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SELECT * FROM simplex.playlists ORDER BY title DESC;
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异常：ORDER BY is only supported when the partition key is restricted by an EQ or an IN.
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SELECT * FROM simplex.playlists where num=1 ORDER BY title DESC;
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异常：PRIMARY KEY part num cannot be restricted (preceding part title is either not restricted or by a non-EQ relation
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SELECT * FROM simplex.playlists where title='La Petite Tonkinoise' ORDER BY title DESC;
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异常：ORDER BY is only supported when the partition key is restricted by an EQ or an IN.
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SELECT * FROM simplex.playlists where id=2cc9ccb7-6221-4ccb-8387-f22b6a1b354d ORDER BY id DESC;
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异常：Order by is currently only supported on the clustered columns of the PRIMARY KEY, got id
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SELECT * FROM simplex.playlists where title='La Petite Tonkinoise' ORDER BY num DESC;
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异常：ORDER BY is only supported when the partition key is restricted by an EQ or an IN.
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通过以上实验可以得出cassandra cql order by 字段必须是复合主键的第二个字段，并且需要where后跟上第一个字段的条件判断。
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另外：CLUSTERING ORDER
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 官方说明 
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 if the table has been defined without any specific CLUSTERING ORDER, then then allowed orderings are the order induced by the clustering key and the reverse of that one. 
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 otherwise, the orderings allowed are the order of the CLUSTERING ORDER option and the reversed one. 
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